1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to improving a dynamic range of an image, and more particularly, to improving a dynamic range of an image of a digital image capture device using a sensor by individually adjusting a duration of an integration time on a line by line basis and applying interpolation filtering in consideration of correlation between a current line and neighboring lines.
2. Description of the Related Art
Image capture devices have limited dynamic range and hence are not able to capture an entire illumination range present in a natural scene. When an image has a limited dynamic range, pixels of the image may be placed at either a dark or light side of a histogram of the image. In this case, even in parts of the image which have different brightness, a darker area of the image may have a narrow dynamic range, or the light may saturate in a lighter area so that an object in the image is hard to recognize. In an extreme case, even when there is an object in the image, the object cannot be seen due to the limited dynamic range.
A digital image capture device obtains an image by converting the light collected by a sensor unit into electronic signals. The digital image capture device generally captures an image in a natural scene intact, and can also obtain a darker or lighter image than the actual image according to the duration of an integration time for which the light is collected. In other words, the digital image capture device can obtain a lighter image as the device collects the light for a longer period of time. Therefore, it can be assumed that the darker area has a shorter integration time and the lighter area has a longer integration time.
FIG. 1 shows an actual dynamic range 102 of a natural scene to be captured and a dynamic range 112 of an image capture device.
The dynamic range 102 is an actual dynamic range of the natural scene to be captured, and the dynamic range 112 is a dynamic range of the image capture device. The image capture device has a limited dynamic range which cannot include the entire actual dynamic range of the natural scene. Especially, since in a digital image, which is an 8-bit image, brightness levels are represented by only 0 to 255, the dynamic range of the digital device is not sufficient to represent the natural scene intact.
Thus, parts of the actual dynamic range 102 may not lie within the dynamic range 112 of the image capture device. A range 104 between X and X′ corresponds to a dark range of the natural scene, and a range 106 between Y′ and Y corresponds to a light range of the natural scene.
In the dynamic range 112 of the image capture device, the range 104 is represented as X which indicates a darkest value of the dynamic range 112, and thus objects in the natural scene within this range are recognized as having the same brightness so that it is difficult to identify the object clearly.
In the same manner, the range 106 is represented by Y which indicates the lightest value of the dynamic range 112 of the image capture device, and thus light saturates an image within this range so that it is impossible to recognize objects in the image.
In order to represent an image naturally as well as improve a limited dynamic range, it is important to stretch brightness contrast of an object appropriately, and conventionally, histogram stretching is generally used to improve the brightness contrast of an image.
However, since the conventional stretching method uses maximum and minimum values of pixels, when there is excessively dark or excessively light noise present in the image, a dynamic range is adjusted, not by the actual brightness, but by the noise, and thus there is a problem in that the result is not desirable. Moreover, when there are artifact pixels, input values of the artifact pixels are 0, and thus, the minimum value of the input pixels becomes 0, and a dynamic range is, therefore, controlled, not by the actual brightness, but by the artifact pixels. Besides such cases where noise or artifact pixels are present in an image, since the amount of lightening or darkening is small, the result of adjusting the dynamic range is not beneficial.